U.S. patent number 5,973,406 [Application Number 08/918,019] was granted by the patent office on 1999-10-26 for electronic device bonding method and electronic circuit apparatus.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Masahide Harada, Toru Nishikawa, Ryohei Satoh, Mitsugu Shirai, Takayuki Uda, Osamu Yamada.
United States Patent |
5,973,406 |
Harada , et al. |
October 26, 1999 |
Electronic device bonding method and electronic circuit
apparatus
Abstract
An electronic device is solder bonded properly without using
fluxes nor precise positioning with respect to a substrate. A bond
pad with a size about twice the size of terminal pad of the
electronic device is formed in a region on the substrate where the
electronic device is to be mounted. After placing the electronic
device of the substrate surface, the whole unit is heated in a
nitrogen atmosphere to melt a bump formed on the terminal pad of
the electronic device. The molten solder wets and spreads over the
bond pads formed on the substrate, thereby establishing reflow
soldering between the bond pads and the terminal pads. The position
of the electronic device with respect to the substrate is
spontaneously corrected due to a self-alignment function induced by
wetting and spreading of the molten solder over the bond pad of the
substrate.
Inventors: |
Harada; Masahide (Yokohama,
JP), Nishikawa; Toru (Yokohama, JP), Satoh;
Ryohei (Yokohama, JP), Yamada; Osamu (Hiratsuka,
JP), Uda; Takayuki (Hadano, JP), Shirai;
Mitsugu (Hadano, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
16804833 |
Appl.
No.: |
08/918,019 |
Filed: |
August 25, 1997 |
Foreign Application Priority Data
|
|
|
|
|
Aug 26, 1996 [JP] |
|
|
8-223859 |
|
Current U.S.
Class: |
257/780; 257/737;
438/613; 438/612; 257/E21.511 |
Current CPC
Class: |
H01L
24/81 (20130101); H05K 3/3436 (20130101); H01L
2924/01029 (20130101); H01L 2224/81136 (20130101); H01L
2924/01075 (20130101); H01L 2924/01006 (20130101); H01L
2924/14 (20130101); H01L 2924/014 (20130101); H01L
2924/0105 (20130101); H01L 2924/01047 (20130101); H01L
2924/01082 (20130101); H01L 2924/01079 (20130101); H01L
2224/81801 (20130101); Y02P 70/50 (20151101); H05K
2203/0182 (20130101); H01L 2924/01327 (20130101); H05K
2201/2036 (20130101); Y02P 70/613 (20151101); H01L
2224/17517 (20130101); H05K 2203/086 (20130101); H05K
2201/09781 (20130101); H01L 2224/8114 (20130101); H01L
2924/01033 (20130101); H01L 2224/13111 (20130101); H01L
2924/01051 (20130101) |
Current International
Class: |
H01L
21/02 (20060101); H05K 3/34 (20060101); H01L
21/60 (20060101); H01L 023/48 () |
Field of
Search: |
;438/613,614,615,612
;257/780,737,738 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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56-78356 |
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Jun 1981 |
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JP |
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59-225893 |
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Dec 1984 |
|
JP |
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64-10634 |
|
Jan 1989 |
|
JP |
|
2-152246 |
|
Jun 1990 |
|
JP |
|
2-290693 |
|
Nov 1990 |
|
JP |
|
4-220168 |
|
Aug 1992 |
|
JP |
|
6-041601 |
|
Feb 1994 |
|
JP |
|
6-291457 |
|
Oct 1994 |
|
JP |
|
8-108292 |
|
Apr 1996 |
|
JP |
|
8-162753 |
|
Jun 1996 |
|
JP |
|
8-293665 |
|
Nov 1996 |
|
JP |
|
WO97/32457 |
|
Apr 1997 |
|
WO |
|
Other References
1st Symposium "Microjoining and Assembly Technology in
Electronics", Feb. 9-10, 1995, pp. 187-192..
|
Primary Examiner: Everhart; Caridad
Attorney, Agent or Firm: Fay, Sharpe, Beall, Fagan, Minnich
& McKee
Claims
What is claimed is:
1. An electronic device bonding method by which bumps formed on
terminal pads of an electronic device are melted to form solder
joints so as to connect said bond pads of device mounting pattern
formed on a substrate and said terminal pads of said electronic
device, comprising the steps of:
fabricating said device mounting pattern which comprises a
plurality of said bond pads, each having a surface area about twice
a size of a corresponding one of said terminal pads of said
electronic device, within a surface region of said substrate where
said electronic device is to be mounted; and
melting said bumps formed on said terminal pads of said electronic
device while said bumps contact with the corresponding bond pads of
said device mounting pattern fabricated on said substrate so as to
form solder joints connecting between said bond pads of said device
mounting pattern fabricated on said substrate and said terminal
pads of said electronic device.
2. An electronic device bonding method by which bumps formed on a
plurality of terminal pads of an electronic device are melted to
form solder joints so as to connect bond pads of a device mounting
pattern formed on a substrate and said terminal pads of said
electronic device, comprising the steps of:
fabricating said device mounting pattern which comprises a
plurality of said bond pads, each having a larger surface area than
a corresponding terminal pad of said electronic device, within a
surface region of said substrate where said electronic device is to
be mounted;
melting said bumps formed on said terminal pads of said electronic
device while said bumps contact with corresponding bond pads of
said device mounting pattern fabricated on said substrate so as to
form solder joints connecting between said bond pads of said device
mounting pattern fabricated on said substrate and said terminal
pads of said electronic device; and,
wherein at least one of said bumps formed on at least one of the
plurality of said terminal pads of said electronic device is an
electronic device push-up bump, which contacts with a surface
region of said substrate where no bond pad is formed when said
electronic device is mounted on said substrate, and the melted
push-up bump pushes said electronic device up by its surface
tension during the formation of said solder joints.
3. The electronic device bonding method in accordance with claim 2,
wherein,
said surface region of said substrate, where no bond pad is formed
and to which said electronic device push-up bump contacts, includes
areas in the center and the periphery of the region where said
electronic device is to be mounted.
4. The electronic device bonding method in accordance with claim 2,
wherein,
said solder joints, which bond between said bond pads formed on
said substrate and a part of said terminal pads on which said
push-up bump has not been formed, form a drum type shape.
5. An electronic circuit apparatus in which solder joints are
formed between bonds pads of a device mounting pattern formed on a
substrate and terminal pads of an electronic device using a
flip-chip method, wherein:
said bond pad of said device mounting pattern formed on said
substrate has a surface area about twice a size of a corresponding
terminal pad of said electronic device.
6. An electronic circuit apparatus in which solder joints are
formed between bonds pads of a device mounting pattern formed on a
substrate and a plurality of terminal pads of an electronic device
using a flip-chip method, wherein:
said bond pad of said device mounting pattern formed on said
substrate has a larger surface area than a corresponding terminal
pad of said electronic device;
at least one of said bumps formed on the plurality of said terminal
pads said electronic device is an electronic device push-up bump,
which contacts with a surface region of said substrate where no
bond pad is formed when said electronic device is mounted on said
substrate, and the melted push-up bump pushes said electronic
device up by its surface tension during the formation of said
solder joints; and,
said solder joints, which bond between said bond pads formed on
said substrate and said terminal pads on which said push-up bump
has not been formed, form a drum type shape.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related to a bonding method of electronic circuit
devices.
2. Description of Related Art
When some of electronic devices in an apparatus become unnecessary
due to a change in specification or the like and are required to be
removed from their substrates, it is typical to conduct re-heating
of solder joints bonding between terminal pads of these unnecessary
electronic devices and bond pads of a device mounting pattern
formed on the substrates.
However, at the same time, the re-heating of solder joints induces
the formation of intermetallic compound layers of less wettability
on the bond pads of the device mounting pattern on the substrate.
This becomes a problem since these intermetallic compound layers
prevent terminal pads of newly mounted electronic devices from
creating stable bonds.
Japanese Patent Application Publication (KOKAI) No. 64-10634
suggested a semiconductor integrated circuit apparatus in which
electronic devices may be removed from a substrate by using
mechanical force without damaging the substrate to be recycled.
In the semiconductor integrated circuit apparatus of prior art,
terminal pads of the electronic devices are soldered on the
corresponding bond pads of the device mounting pattern formed on
the substrate using a face down bonding method. Here, each of the
bond pads of the device mounting pattern is provided so as to have
a larger surface area compared to the corresponding terminal pad of
the electronic device so as that the mechanical force (the force to
break the solder joint) applied during the removal of the
electronic device may be concentrated toward a side of the
electronic device.
Accordingly, the substrate to be recycled is hardly damaged while
the unnecessary electronic devices may be destroyed. This type of
solder bonding has an advantage when frequent replacements of the
electronic devices mounted on the substrate are anticipated.
There is another method of bonding between the bond pads of the
device mounting pattern formed on the substrate and the terminal
pads of the electronic devices. It is known as a flip-chip method
in which solder bumps formed on the terminal pads of the electronic
devices are melted to form bonding between the terminal pads of the
electronic devices and the bond pads of the device mounting pattern
formed on the substrate so as to establish electrical connections
between them.
The flip-chip method has an advantage in that the electronic device
may be soldered with an appropriate attitude at a predetermined
location since a position of the electronic device with respect to
the substrate is self-aligned due to a surface tension of the
molten solder.
In order to fully utilize the self-alignment function in the prior
art, it is necessary to remove an oxidized film on the surface of
the solder bump formed on the terminal pad of the electronic device
before the soldering, by applying fluxes on the solder bump.
Reliability of the electronic circuit apparatus which is the final
product largely depends on the stability of bonds between the
device mounting pattern and the terminal pads of the electronic
device. The published specification of Japanese Utility Model
Application No. 54-155903 teaches a semiconductor chip mount body
in which optimization in the shape of solder joint, which bonds
between the bond pads of the device mounting pattern formed on the
substrate and the terminal pad of the electronic device, is
attempted so as to provide long term stability of the bond.
As shown in FIG. 8A, insulation pads 814 are formed on a substrate
804 used in the semiconductor chip mount body at positions which do
not correspond to any terminal pads 802 of an electronic device
801, in addition to bond pads 805 of a device mounting pattern. To
mount the electronic device 801, solder pastes 815 are printed in a
sheet-like form on the insulation pads 814. The solder paste 815
has a higher melting point than that of solder bumps 806, 807
formed on the terminal pads 802 of the electronic device 801 and
the bond pads 805 of the device mounting pattern.
The flux is applied on each of the solder bumps 806 formed on the
terminal pads 802 of the electronic device 801 and the solder bumps
807 formed on the bond pads 805 of the substrate 804 to remove the
surface oxidized film.
After the electronic device 801 is disposed on the substrate 804 at
a predetermined position, both of them are heated up to a
predetermined temperature. The solder bumps 806, 807 formed on the
terminal pads 802 and the bond pads 805 melt first. The molten
solder wets and spreads over surfaces of the bond pad 805 formed on
the substrate 804 and the terminal pad 802 of the electronic device
801, as shown in FIG. 8B.
Then, as shown in FIG. 8C, the solder sheets 815 begin to melt.
Here, the molten solder sheets 815 do not wet or spread over the
surface of the electronic device 801. The molten solder sheets 815
hold up the electronic device 801 by their surface tensions,
thereby causing the solder joints 809 to form a drum type shape or
a pillar type shape, both of which are stable against external
stresses, between the bond pads 805 formed on the substrate 804 and
the terminal pads 802 of the electronic device 801.
SUMMARY OF THE INVENTION
However, an effective utilization of the self-alignment function
during formation of solder joints is not included in any of the
objectives of Japanese Patent Application Publication (KOKAI) No.
64-10634 which discloses the semiconductor integrated circuit
apparatus.
The use of fluxes is required in the semiconductor chip mount body
disclosed in the published specification of Japanese Utility Model
Application No. 54-155903 to remove the oxidized film formed on the
surface of the solder bump 806 formed on the terminal pad 802 of
the electronic device 801 and on the solder bump 807 formed on the
bond pads 805 of the device mounting pattern of the substrate 804.
A residue of the fluxes may sometimes cause corrosion of the solder
joint. If this happens, performance of the semiconductor chip mount
body which becomes the final product may be impaired.
Further, the prior art of the published specification of Japanese
Utility Model Application No. 54-155903 requires additional
fabrication process steps since it is necessary to provide
different types of solders with different melting points on the
bond pad 805 of the device mounting pattern of the substrate 804
and the insulation pad 814.
An object of the present invention is to provide a fluxless solder
bonding method by which an electronic device may be soldered
properly without precise positioning of the electronic device with
respect to a substrate in advance.
Another object of the present invention is to form solder joints
which are stable in the long term using the above fluxless solder
bonding method without increasing a number of fabrication process
steps.
The above objects of the present invention are accomplished by an
electronic device bonding method by which bumps formed on terminal
pads of an electronic device are melted to form solder joints so as
to connect the terminal pads of the electronic device and bond pads
of a device mounting pattern formed on the substrate, comprising
the steps of: fabricating the device mounting pattern which
comprises a plurality of bond pads, each of which has a larger
surface area than the corresponding terminal pad of the electronic
device, within a region of the substrate surface where the
electronic device is to be mounted; and melting the bumps formed on
the terminal pads of the electronic device with the bumps formed on
the terminal pads of the electronic device contacting with the
corresponding bond pads of the device mounting pattern fabricated
on the substrate so as to form solder joints bonding between the
bond pads of the device mounting pattern fabricated on the
substrate and the terminal pads of the electronic device.
According to the present invention, when the bumps formed on the
terminal pads of the electronic device are being melted, a position
of the electronic device with respect to the substrate is
spontaneously corrected by a force induced during wetting and
spreading of the molten bumps over the bond pads of the substrate
because of the above feature. Therefore it becomes possible to
solder bond the electronic device at a proper position on the
substrate without precise positioning of the electronic device with
respect to the substrate in advance.
According to the present invention, wetting and spreading of the
molten solder on the bond pads of the device mounting pattern of
the substrate are highly promoted since each of the bond pads
occupies a larger surface area than the corresponding terminal pad
of the electronic device. Thus, it become possible to maximize the
self-alignment function, thereby eliminating the need of flux
application on the solder bumps formed on the terminal pads of the
electronic device in advance.
In the present invention, when the electronic device with a
plurality of terminal pads is used, a bump formed on at least one
of the terminal pads may be a push-up bump for pushing up the
electronic device. The push-up bump comes into contact with a
surface region of the substrate where no bond pad of the device
mounting pattern is formed when the electronic device is mounted on
the substrate. The push-up bump is melted during the formation of
the solder joint, thereby pushing up the electronic device by its
surface tension.
Therefore, the solder joint of a drum type shape which is stable
against external stresses, i.e. the solder joint of a long term
stability may be formed between the bond pad of the device mounting
pattern formed on the substrate and the terminal pad of the
electronic device without increasing the number of fabrication
process steps.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a front view of an electronic device according to the
first embodiment of the present invention;
FIG. 1B is a side view of an electronic device according to the
first embodiment of the present invention;
FIG. 2A is a front view of a substrate according to the first
embodiment;
FIG. 2B is a side view of a substrate according to the first
embodiment;
FIG. 3 is an explanatory view for an illustration of a fitting step
during a solder bonding process in an electronic device bonding
method according to the first embodiment;
FIG. 4 is an explanatory view for an illustration of the solder
bonding process in the electronic device bonding method according
to the first embodiment;
FIG. 5A is a front view of the substrate according to the second
embodiment of the present invention;
FIG. 5B is a side view of the substrate according to the second
embodiment of the present invention;
FIG. 6 is an explanatory view for an illustration of an fitting
step during an solder bonding process in an electronic device
bonding method according to the second embodiment;
FIG. 7 is an explanatory view for an illustration of the solder
bonding process in the electronic device bonding method according
to the second embodiment; and
FIG. 8A is an explanatory view for an illustration of the solder
bonding process of the prior art.
FIG. 8B is an explanatory view for an illustration of the solder
bonding process of the prior art.
FIG. 8C is an explanatory view for an illustration of the solder
bonding process of the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The first embodiment of the present invention will now be
explained.
First, an electronic device and a substrate used in the embodiment
will be explained with reference to FIGS. 1A, 1B, 2A, and 2B.
A metallic film (metallization) with a two-layer structure is
formed using a vapor-deposition method on each of the terminal pads
2 of the electronic device 1 as shown in FIGS. 1A and 1B. The
electronic device 1 may be, for example, an LSI chip or the like.
The first layer of the metallic film is composed of a metallic
substance, such as Ni-Cu alloy or the like, which is highly
adhesive to the terminal pad 2 and has a slow rate of reaction with
solder. The second layer of the metallic film is composed of a
metallic substance, such as Au or the like, which is highly
wettable with a bump substance.
Each of the bond pads 4 of the device mounting pattern is formed on
the substrate 3 shown in FIGS. 2A and 2B at a position
corresponding to the terminal pad 2 of the electronic device 1 with
each of the bond pads 4 having a larger surface area than that of
the corresponding terminal pad 2 of the electronic device 1. For
example, the surface area of the bond pad 4 may be a predetermined
number of times larger than that of the terminal pad 2. Further, a
metallization similar to that of the terminal pad 2 of the
electronic device 1 is formed on each of the bond pads 4.
The electronic device bonding method, by which the terminal pads 2
of the electronic device 1 are solder bonded on the bond pads 4 of
the device mounting pattern formed on the substrate 3, will now be
explained with reference to FIGS. 3 and 4.
First, the bump 5 is formed on each of the terminal pads 2 of the
electronic device 1 by depositing solder onto the terminal pads 2
using a bump fabrication technique of the prior art, such as the
vapor deposition method. Preferably, 63Sn37Pb (composition of 37%
Pb, 63% Sn) or 98Pb2Sn (composition of 98% Pb, 2% Sn) or
96.5Sn3.5Ag (composition of 96.5% Sn, 3.5% Ag) may be used as the
solder substance.
After placing the electronic device 1 at a predetermined position
of the substrate 3, the whole unit is heated in a nitrogen
atmosphere to melt the bumps 5 formed on the terminal pads 2 of the
electronic device 1 as shown in FIG. 3. The molten solder 6 wets
and spreads over the bond pads 4 formed on the substrate 3 as shown
in FIG. 4, thereby establishing the reflow soldering between the
bond pads 4 formed on the substrate 3 and the terminal pads 2 of
the electronic device 1.
A typical heating temperature of not less than the melting point
(183.degree. C.) and not more than 215.degree. C., and a typical
heating period of about 3 minutes may be employed when 63Sn37Pb is
selected as the solder substance. A typical heating temperature of
not less than the melting point (320.degree. C.) and not more than
360.degree. C., and a typical heating period of about 3 minutes may
be employed when 98b2Sn is selected as the solder substance. A
typical heating temperature of not less than the melting point
(221.degree. C.) and not more than 245.degree. C., and a typical
heating period of about 3 minutes may be employed when 96.5Sn3.5Ag
is selected as the solder substance.
As the molten solder wets and spreads over each of the bond pads 4
formed on the substrate 3, the self-alignment function becomes
effective, and a minor misalignment that may have occurred during
the initial positioning of the electronic device 1 with respect to
the substrate 3 may be spontaneously corrected. As a result, the
electronic device 1 is properly solder bonded on the substrate 3.
Thus, according to the present embodiment, the fluxless bonding,
which is explained in the section of DESCRIPTION OF RELATED ART as
it has an advantage in replacing electronic devices on the
substrate, may be formed without precise positioning of the
electronic device with respect to the substrate in advance.
The self-alignment function still becomes effective even without
applying the flux in advance on the bumps 5 formed on the terminal
pads 2 of the electronic device 1 because each of the bond pads 4
of the device mounting pattern formed on the substrate 3 is
provided so as to have a larger surface area than the corresponding
terminal pad 2 of the electronic device 1. This feature
significantly improves abilities of wetting and spreading of the
molten solder over the bond pads 4 formed on the substrate 3.
This has been proved quantitatively by inspecting an electronic
circuit apparatus manufactured according to the present
embodiment.
The inventors of the present invention prepared several types of
substrates, each having 490 bond pads with a size varied for
different types of substrate. Ten electronic devices (LSI chips),
each having 490 terminal pads (diameter 130 .mu.m), are solder
bonded on each type of substrate. Then, positions of the soldered
LSI chips on each of the substrate are inspected.
The inspection revealed that only two of the electronic devices
were soldered at the proper positions on the substrate with the
bond pad of the same size as the terminal pad of the electronic
device. On the other hand, more of the electronic devices were
soldered at the proper position on the substrate with the bond pad
which had a larger size than the terminal pad of the electronic
device. That is, a clear improvement of the self-alignment function
due to an enlargement of the bond pad of the device mounting
pattern formed on the substrate has been confirmed.
Particularly on the substrates with the bond pads each having a
size larger than about twice the size of the terminal pad of the
electronic device, all of the electronic devices, or nearly all of
them on the substrate, were soldered at the proper positions. At a
practical level, however, it is recommended to use the bond pad of
the device mounting pattern with a size about twice the size of the
corresponding terminal pad of the electronic device when a recent
tendency to utilize a finer pitch for the terminal pads of the
electronic device is taken into consideration. For example, a bond
pad with a diameter of 200 .mu.m may be employed for a terminal pad
with a diameter of 130 .mu.m.
The second embodiment of the present invention will now be
explained.
In the present embodiment, the substrate 3 shown in FIGS. 5A, 5B is
used instead of the substrate 3 shown in FIG. 2A, 2B in order to
optimize a shape of the solder joint which bonds between the bond
pad 4 of the device mounting pattern formed on the substrate 3 and
the terminal pad 2 of the electronic device 1. The explanation is
as follows.
The bond pads 4 with a larger surface area than the corresponding
terminal pads 2 of the electronic device 1 to be mounted (as
mentioned above, preferably more than about twice the size) are
formed on the substrate 3 of FIGS. 5A, 5B in a similar way to that
of the substrate 3 of FIGS. 2A, 2B. Further, a metallization
similar to that of the previous embodiment is formed on each of the
bond pads 4 of the device mounting pattern which is formed on the
substrate 3.
An array of the bond pads 4 of the device mounting pattern formed
within a predetermined region of the substrate 3 shown in FIGS. 5A,
SB is fabricated so that it has the same array structure as that of
the terminal pads 2 of the electronic device 1 to be mounted in the
region, except for parts of which that have been omitted. More
concretely, the substrate 3 is provided so as to have vacant areas,
in which a predetermined number of bond pads (typically, a total of
20 bond pads) could have been formed, near the center and periphery
of the region where the electronic device 1 is to be mounted.
As shown in FIG. 6, when the electronic devices 1 are placed on the
substrate 3, bumps 5b formed on a part of the terminal pads of the
electronic device 1 contact with the corresponding bond pads 4
formed on the substrate 3 while bumps 5a formed on the rest of the
terminal pads contact with surface areas of the substrate 3 where
no bond pad 4 is formed.
As shown in FIG. 7, when the whole unit is heated, the bumps 5b
formed on the part of the terminal pads start to melt, and rapidly
wet and spread over the bond pads 4 formed on the substrate 3 even
though no flux was applied, while molten bumps 5a on the rest of
the terminal pads do not wet nor spread over the surface of the
substrate 3 and are gradually condensed into ball shaped bodies 7.
This causes a gradual separation of the electronic device 1 from
the substrate 3 due to the surface tension induced by the ball
shaped bodies 7. As a result, the solder joints 6 with a drum type
shape or a pillar type shape, which are stable against external
stresses, are formed in between the part of the terminal pad of the
electronic device 1 and the bond pads 4 of the device mounting
pattern of the substrate 3.
This has been quantitatively verified by inspecting an electronic
circuit apparatus manufactured according to the present
embodiment.
The inventors of the present invention performed a temperature
cycling test (-50.degree. C..about.125.degree. C.) on two types of
electronic circuit apparatuses, one of which is manufactured using
the substrate 3 having the bond pads (250 .mu.m in diameter)
arrayed as shown in FIG. 2A, 2B and the electronic device having
the terminal pads (150 .mu.m in diameter) arrayed as shown in FIG.
1A, 1B, and the other using the substrate 3 having the bond pads
(250 .mu.m in diameter) arrayed as shown in FIGS. 5A, SB and the
electronic device having the terminal pads (150 .mu.m in diameter)
arrayed as shown in FIG. 1A, 1B.
The result showed that a variation (increase) in a resistance of
the solder joint started to be observed as early as the 1000th
cycle of the temperature cycling test for the electronic circuit
apparatus manufactured using the substrate 3 shown in FIG. 2A, 2B
and the electronic device 1 shown in FIG. 1A, 1B. In contrast,
almost no variation in the resistance of the solder joint was
observed even after 1000th cycle of the temperature cycling test
for the electronic circuit apparatus manufactured using the
substrate 3 shown in FIGS. 5A, 5B and the electronic device 1 shown
in FIG. 1A, 1B. This clearly indicates an improvement in
reliability of the solder joint.
Here, the same self-alignment function as that of the first
embodiment is also effective in the present invention.
Accordingly, the present embodiment enables the formation of a
solder joint with a long term stability, simply by modifying the
substrate 3 to be used and without changing the number of the
fabrication process steps. For example, the fabrication process of
the present embodiment becomes much simpler than that of the
semiconductor chip mount body disclosed in the published
specification of Japanese Utility Model Application No. 54-155903
described in DESCRIPTION OF RELATED ART, since no bump using two
types of solders is required in the present embodiment.
According to the present invention, the electronic device may be
solder bonded properly without using the flux nor precise
positioning of the electronic device with respect to the substrate
in advance. Further according to the present invention, by
modifying the array structure of the bond pads of the device
mounting pattern of the substrate to be used, the solder joint with
a long term stability may be formed without increasing a number of
the fabrication process steps.
* * * * *